Muslims around the world are due Saturday to observe the holy day of Ashura, which is known to some as a day of self-flagellation and fasting but which otherwise is not always well understood. Here are answers to common questions about what Ashura actually is, its history, the traditional ways its commemorated and why.

Ashura, which in Arabic means “tenth,” falls on the tenth day of the Islamic month of Muharram, which this year began Oct. 15. Every year, the lunar-based Islamic calendar shifts forward roughly 11 days, and so Islamic holidays shift accordingly. Ashura is slated to fall on Oct. 24, although observance typically begins the night before, which this year means Friday evening. All Muslims commemorate Ashura, but Sunnis and Shiites, or those who belong to the religion's two major sects, mark Ashura differently.

Ashura is said to have been based on Yom Kippur, the Jewish Day of Atonement, and for Sunni Muslims, some of whom voluntarily fast on Ashura, atonement is what the day represents. “Fasting on the Ashura day is atonement for sins,” the Center of Fatwa of the General Authority for Islamic Affairs and Awqaf in the United Arab Emirates said in a decree.

But Ashura is perhaps best known as being a significant, if bloody, holy day for Shiites. It marks the day that Hussein, the grandson of the Prophet Muhammad, founder of Islam, was martyred in 680 AD in Karbala, southwest of modern-day Baghdad, Iraq. Shiites commemorate Ashura by publicly expressing grief, making pilgrimages to Karbala and carrying out passion plays and re-enactments.

Likely the most famous Shiite tradition for Ashura is self-flagellation, which is typically carried out by men. This practice is aimed at mimicking the suffering of Hussein. Some men will beat themselves with chains, while others cut themselves on their foreheads until blood begins to flow. 

The death of Hussein was a defining event in Islamic history because it helped further cement the division of Islam into the two major sects that exist today. After the death of the Prophet Muhammad, Islam's founder, in 632 AD, Muslims began to disagree over who should succeed him. Shiites supported Ali, the son-in-law of the Prophet and father of Hussein, to be ruler of the Muslim community, but Sunnis did not support Ali. Ali eventually became the fourth caliph, or leader of the Muslim community, but not before a lasting violence had broken out between the two sides. 

In 680 AD, Hussein, who supported his father, was decapitated and his followers were killed at the Battle of Karbala, an event that among Shiites still resonates today. The two groups have their theological differences, and the Shiite community sees itself as “a persecuted yet righteous minority surrounded by a persecuting and unjust Sunni majority,” Reza Aslan, an author and scholar on Islam, has explained. Today, Shiite Muslims comprise approximately 10 to 15 percent of the world’s Muslims.